The new Windows Phone Mango SDK introduced a testing tool, that is tied to the device emulator, allowing developers to simulate location data and readings from the accelerometer sensor (now it also allows taking screenshots). What would be great is having custom motions that can later on be tested multiple times with multiple applications. If you copy custom motions to the acc folder while the testing tool is running, you will have to close the testing tool (the emulator can continue running) and re-open it again for new motions to be shown in the list.